‡ See Calcium Supplements (Systemic) for systemic use of calcium carbonate in hypocalcemia§ See Laxatives (Local) for laxative use of magnesium hydroxide and magnesium oxideNote: For a listing of dosage forms and brand names by country availability, see Dosage Forms section(s).

Note: Bracketed information in the Indications section refers to uses that are not included in U.S. product labeling.Accepted

Hyperacidity (treatment)
Ulcer, duodenal (treatment) or
Ulcer, gastric (treatment)—Antacids are indicated for relief of symptoms associated with hyperacidity (heartburn, acid indigestion, and sour stomach). In addition, antacids are used in hyperacidity associated with gastric and duodenal ulcers. However, there have been reports of increased gastrin levels and increased gastric secretion (acid rebound) associated with the use of antacids. {15}{31}{87}
—Some of the antacid combinations contain other ingredients that have no antacid properties. Simethicone, an antiflatulent, has been added as an aid in those conditions in which the retention of gas may be a problem; however, in the treatment of peptic ulcer diseases, the advantage of using antacid and simethicone combinations rather than antacids alone has not been clearly established. {31}

[Hyperphosphatemia (treatment)]1—Aluminum carbonate and aluminum hydroxide may be used in conjunction with a low-phosphate diet to reduce elevated phosphate levels and demineralization of bones in patients with renal insufficiency. {31} However, use of aluminum-containing antacids as phosphate binders may lead to aluminum toxicity in patients with renal insufficiency. {77}{89}{90} Other agents may be preferable for treating hyperphosphatemia in patients with renal insufficiency.

—[Aluminum hydroxide has been used in the treatment of neonatal hypocalcemia and diarrhea; however, it generally has been replaced by other agents. Aluminum carbonate and aluminum hydroxide have been used along with a low-phosphate diet to prevent formation of phosphatic (struvite) urinary stones; however, their use has been replaced by other agents.{104} Magnesium hydroxide has been used to prevent recurrence of calcium stones; however, it has been replaced by other agents.{104} Use of aluminum-containing antacids in young children and premature infants may lead to aluminum toxicity, especially in those patients with renal failure.{46}{76}{77}]1Unaccepted
Antacids have been used in patients undergoing anesthesia or during labor to lessen the danger from aspiration of gastric contents. However, the use of antacids to prevent acid aspiration has generally been replaced by the equally or more effective histamine H 2-receptor antagonists or citrate solutions. {07}{42}

Antacid—These medications react chemically to neutralize or buffer existing quantities of stomach acid but have no direct effect on its output. This action results in increased pH value of stomach contents, thus providing relief of hyperacidity symptoms. Also, these medications reduce acid concentration within the lumen of the esophagus. This causes an increase in intra-esophageal pH and a decrease in pepsin activity. {69}

Antiurolithic—Aluminum carbonate and aluminum hydroxide bind phosphate ions in the intestine to form insoluble aluminum phosphate, which is excreted in the feces. {69} They thereby reduce phosphates in the urine and prevent formation of phosphatic (struvite) urinary stones. Magnesium hydroxide inhibits the precipitation of calcium oxalate and calcium phosphate, thus preventing the formation of calcium stones.

Antihyperphosphatemic—Aluminum carbonate and aluminum hydroxide reduce serum phosphate levels by binding with phosphate ions in the intestine to form insoluble aluminum phosphate, which passes through the intestinal tract unabsorbed. {69}

Antihypocalcemic—Aluminum hydroxide may increase the release of calcium from bone {68} as a result of the decreased serum phosphate levels.

Antacids may increase lower esophageal sphincter (LES) pressure. {05} Aluminum-containing antacids have a cytoprotective effect on the gastric mucosa that may be associated with the stimulation of prostaglandin secretion, thus providing protection against mucosal necrosis and hemorrhage caused by corrosive agents, such as aspirin and ethanol. {91}{92}Absorption:

Aluminum-containing—Small amounts of the aluminum in aluminum hydroxide are absorbed from the intestine. {93}

Calcium-containing—Approximately 15% of the calcium in calcium carbonate is absorbed from the intestine in normal persons. {93} The amount of calcium absorbed from the gastrointestinal tract is determined by hormonal factors, particularly parathyroid hormone, and vitamin D. {93}

Magnesium-containing—Approximately 10% of the magnesium in magnesium hydroxide (magnesia) is absorbed from the intestine.Onset and duration of action

Onset of action is dependent upon the ability of the antacid to solubilize in the stomach and react with the hydrochloric acid. {69} The poorly soluble antacids (e.g., magnesium trisilicate) {69} will thus react more slowly with hydrochloric acid than will the more soluble ones. In most cases with slow-acting antacids, the onset of action is delayed and may not take place if gastric emptying is rapid. {31}

Duration of action is determined primarily by gastric emptying time. Depending on the kind of antacid used, the duration of action in fasting patients may range from 20 to 60 minutes. {69} However, when the antacid is given 1 hour after meals, the acid-neutralizing effect may be prolonged up to 3 hours. {69}

The following table provides a relative comparison of onset and duration of action of different antacids.

* Absorptive properties of the gel prolong its duration of action† If gastric emptying is rapid, stomach may empty before much of the acid is neutralizedElimination:
Renal and fecal; {69}{93} 15 to 30% of the salts formed are absorbed and are then excreted by the kidneys. {69}

Precautions to ConsiderPregnancy/Reproduction

Pregnancy—
Antacids are generally considered safe as long as chronic high doses are avoided. {40}

Aluminum-, calcium-, or magnesium-containing antacids

Adequate and well-controlled studies in humans have not been done; however, there have been reports of antacids causing such adverse effects as hypercalcemia, hypomagnesemia, hypermagnesemia, and increased tendon reflexes in fetuses and/or neonates whose mothers were chronic users of aluminum-, calcium-, and/or magnesium-containing antacids, especially in high doses.

Studies have not been done in animals.

Sodium bicarbonate–containing antacids

Problems in humans have not been documented; however, risk-benefit must be considered because sodium bicarbonate is absorbed systemically. Chronic use may lead to systemic alkalosis. {93} The sodium load that is absorbed can also cause edema and weight gain.

Breast-feeding

Problems in humans have not been documented; although some aluminum, calcium, and magnesium may be distributed into breast milk, the concentration is not great enough to produce an effect in the neonate. {41}Pediatrics

Antacids should not be given to young children (up to 6 years of age) unless prescribed by a physician. Since children are not usually able to describe their symptoms precisely, proper diagnosis should precede the use of an antacid. This will avoid the complication of an existing condition (e.g., appendicitis) or the appearance of severe adverse effects.

Use of magnesium-containing antacids is contraindicated in very young children {102} because there is a risk of hypermagnesemia {94}, especially in dehydrated children or children with renal failure. {68}

Use of aluminum-containing antacids is contraindicated in very young children {102} because there is a risk of aluminum toxicity, especially in dehydrated infants and children or infants and children with renal failure. {76}{77}

Geriatrics

Metabolic bone disease commonly seen in the elderly may be aggravated by the phosphorus depletion {30}, hypercalciuria, and inhibition of absorption of intestinal fluoride caused by the chronic use of aluminum-containing antacids. {79} Also, elderly patients are more likely to have age-related renal function impairment, which may lead to aluminum retention. {67}{102}

Although it is not known whether high intake of aluminum leads to Alzheimer's disease, the use of aluminum-containing antacids in Alzheimer's patients is not generally recommended. Research suggests that aluminum may contribute to the disease's development since it has been found to concentrate in neurofibrillary tangles in brain tissue. {46}{80}{83}Drug interactions and/or related problems
The following drug interactions and/or related problems have been selected on the basis of their potential clinical significance (possible mechanism in parentheses where appropriate)—not necessarily inclusive (» = major clinical significance):

Table 1. Drug Interactions and/or Related Problems

The following drug interactions and/or related problems have been selected on the basis of their potential clinical significance (possible mechanism in parentheses where appropriate)—not necessarily inclusive: (» = major clinical significance)

Note: Combinations containing any of the following medications, depending on the amount present, may also interact with this medication.
Only specific interactions between antacids and other oral medications have been identified in this monograph. However, because of antacids" ability to change gastric or urinary pH and to adsorb or form complexes with other drugs, the rate and/or extent of absorption of other medications may be increased or reduced when the medication is used concurrently with antacids {69}. In general, patients should be advised not to take any other oral medications within 1 to 2 hours of antacids.

Acidifiers, urinary, such as:
Ammonium chloride
Ascorbic acid
Potassium or sodium phosphates
Racemethionine
(antacids may alkalinize the urine and counteract the effect of urinary acidifiers; frequent use of antacids, especially in high doses, is best avoided by patients receiving therapy to acidify the urine)

Amphetamines or {63}
Quinidine
(urinary excretion may be inhibited when these medications are used concurrently with antacids in doses that cause the urine to become alkaline, possibly resulting in toxicity; dosage adjustment may be needed when therapy with these antacids is initiated or discontinued or if dosage is changed) {09}{21}{27}{63}{64}

Anticholinergics or other medications with anticholinergic activity (See Appendix II )
(concurrent use with antacids may decrease absorption, reducing the effectiveness of anticholinergics; doses of these medications should be spaced 1 hour apart from doses of antacids) {63}{68}{69}

(urinary excretion may be delayed by alkalinization of the urine, thus potentiating the side effects of the anticholinergic)

Calcitonin or
Etidronate {70} or
Gallium nitrate {47} or
Pamidronate {108} or
Plicamycin
(concurrent use with calcium carbonate may antagonize the effect of these medications in the treatment of hypercalcemia) {12}

Calcium-containing preparations
(concurrent and prolonged use with sodium bicarbonate may result in the milk-alkali syndrome) {48}{56}{57}{65}

(concurrent use with magnesium-containing antacids may result in binding of magnesium; patients should be advised not to take these medications within 1 hour of cellulose sodium phosphate)

Chenodiol
(concurrent use with aluminum-containing antacids may result in binding of chenodiol, thus decreasing its absorption) {17}

Citrates
(concurrent use with antacids containing aluminum, calcium carbonates, magaldrate, or sodium bicarbonate may result in systemic alkalosis)

(concurrent use of sodium citrate with sodium bicarbonate may promote the development of calcium stones in patients with uric acid stones, due to sodium ion opposition to the hypocalciuric effect of the alkaline load; may also cause hypernatremia) {36}

Digitalis glycosides
(concurrent use with aluminum- and magnesium-containing antacids may inhibit absorption, possibly decreasing plasma concentrations of digitalis glycosides; although actual clinical importance of this interaction has not been established, it is recommended that doses of antacids and digitalis glycosides be separated by several hours) {09}{27}

Diuretics, potassium-depleting, such as bumetanide, ethacrynic acid, furosemide, indapamide, thiazide diuretics {27}
(concurrent use of thiazide diuretics with large doses of calcium carbonate may result in hypercalcemia)

Enteric-coated medications, such as bisacodyl
(concurrent administration of antacids with enteric-coated medications may cause the enteric coating to dissolve too rapidly, resulting in gastric or duodenal irritation) {10}

Ephedrine
(urine alkalinization induced by sodium bicarbonate may increase the half-life of ephedrine and prolong its duration of action, especially if the urine remains alkaline for several days or longer; dosage adjustment of ephedrine may be necessary) {01}{21}

» Fluoroquinolones {06}{14}{19}{20}{53}{74}{85}{88}
(alkalinization of the urine may reduce the solubility of ciprofloxacin and norfloxacin in the urine, especially when the urinary pH exceeds 7.0; if antacids and one of these medications are used concurrently, patients should be observed for signs of crystalluria and nephrotoxicity)

(aluminum- and magnesium-containing antacids may reduce absorption of fluoroquinolones, resulting in lower serum and urine concentrations of these medications; therefore, concurrent use is not recommended; however, if aluminum- and magnesium-containing antacids must be used concurrently with these medications, it is recommended that enoxacin be taken at least 2 hours before or 8 hours after the antacid; ciprofloxacin and lomefloxacin should be taken at least 2 hours before or 6 hours after the antacid; and norfloxacin and ofloxacin should be taken at least 2 hours before or after the antacid)

Folic acid
(prolonged use of aluminum- and/or magnesium-containing antacids may decrease folic acid absorption by raising the pH of the small intestine; patients should be advised to take antacids at least 2 hours after folic acid) {73}{75}

Histamine H 2-receptor antagonists
(concurrent use with antacids may be indicated in the treatment of peptic ulcer to relieve pain; however, simultaneous administration of medium to high doses [80 mmol to 150 mmol] of antacids is not recommended since absorption of histamine H 2-receptor antagonists may be decreased; patients should be advised not to take any antacids within 1/2 to 1 hour of histamine H 2-receptor antagonists) {09}{18}{21}{53}{59}

Iron preparations, oral
(absorption may be decreased when these preparations are used concurrently with magnesium trisilicate or antacids containing carbonate; spacing the doses of the iron preparation as far as possible from doses of the antacid is recommended) {09}{21}{27}{53}

» Isoniazid, oral
(concurrent use with aluminum-containing antacids may delay and decrease absorption of oral isoniazid; concurrent use should be avoided or the patient should be advised to take oral isoniazid at least 1 hour before the antacid) {09}{21}{27}

» Ketoconazole
(antacids may cause increased gastrointestinal pH; concurrent administration with antacids may result in a marked reduction in absorption of ketoconazole; patients should be advised to take antacids at least 3 hours after ketoconazole) {10}{21}

Lithium
(sodium bicarbonate enhances lithium excretion, possibly resulting in decreased efficacy; this may be partly due to the sodium content) {02}{03}{04}{21}

» Mecamylamine
(alkalinization of the urine may slow excretion and prolong the effects of mecamylamine; concurrent use is not recommended) {24}

» Methenamine
(concurrent use with antacids that cause the urine to become alkaline may reduce the effectiveness of methenamine by inhibiting its conversion to formaldehyde; concurrent use is not recommended) {84}

Milk or milk products
(concurrent and prolonged use with calcium carbonate or sodium bicarbonate may result in the milk-alkali syndrome) {48}{56}{57}

Pancrelipase
(concurrent administration of antacids may be required to prevent inactivation of pancrelipase [except enteric-coated dosage forms] {95} by gastric pepsin and acid pH; however, calcium carbonate– and/or magnesium-containing antacids are not recommended since they may decrease the effectiveness of pancrelipase) {26}

Penicillamine
(absorption may be reduced when penicillamine is administered concurrently with aluminum- or magnesium-containing antacids; although more studies are needed to establish the significance of this interaction, it is recommended that doses of antacids and penicillamine be separated by 2 hours) {21}{44}{45}{47}

Phenothiazines, especially chlorpromazine, oral
(absorption may be inhibited when these medications are used concurrently with aluminum- or magnesium-containing antacids; although more studies are needed to establish the significance of this interaction, simultaneous administration should be avoided) {21}

Phenytoin
(concurrent use with aluminum-, magnesium-, and/or calcium carbonate–containing antacids may decrease absorption of phenytoin, thus reducing serum phenytoin concentrations; although more studies are needed to establish the significance of this interaction, it is recommended that doses of antacids and phenytoin be separated by about 2 to 3 hours) {09}{64}{71}{72}

Phosphates, oral
(concurrent use with aluminum- or magnesium-containing antacids may bind the phosphate and prevent its absorption) {61}{62}{65}{66}

(concurrent use with calcium-containing antacids may increase potential of deposition of calcium in soft tissues if serum-ionized calcium is high)

Quinine
(concurrent use with aluminum-containing antacids may decrease or delay the absorption of quinine) {25}{32}

Salicylates
(alkalinization of the urine may increase renal salicylate excretion and lower serum salicylate levels; dosage adjustments of salicylates may be necessary when chronic high-dose antacid therapy is started or stopped, especially in patients receiving large doses of the salicylate, such as patients with rheumatoid arthritis or rheumatic fever) {21}{27}{63}

Sodium bicarbonate or
Vitamin D
(concurrent and prolonged use with calcium carbonate may result in the milk-alkali syndrome) {22}{48}{57}{65}

Sodium fluoride
(concurrent use with aluminum hydroxide may decrease absorption and increase fecal excretion of fluoride)

(calcium ions may complex with and inhibit absorption of fluoride) {29}{65}

» Sodium polystyrene sulfonate resin (SPSR)
(neutralization of gastric acid may be impaired when SPSR is used concurrently with calcium- or magnesium-containing antacids, possibly resulting in systemic alkalosis; concurrent use is not recommended) {21}{27}{58}{64}

Sucralfate
(concurrent use with antacids may be indicated in the treatment of duodenal ulcer to relieve pain; however, simultaneous administration is not recommended since antacids may interfere with binding of sucralfate to the mucosa; patients should be advised not to take any antacids within 1/2 hour before or after sucralfate; concurrent use with aluminum-containing antacids may cause aluminum toxicity in patients with chronic renal failure) {50}{51}

» Tetracyclines, oral
(absorption may be decreased when oral tetracyclines are used concurrently with antacids because of possible formation of nonabsorbable complexes and/or increase in intragastric pH; patients should be advised not to take antacids within 3 to 4 hours of tetracyclines) {09}{21}{27}{53}

Vitamin D, including calcifediol and calcitriol
(concurrent use with magnesium-containing antacids may result in hypermagnesemia, especially in patients with chronic renal failure)

(concurrent use with calcium-containing antacids may result in hypercalcemia) {43}{67}

Laboratory value alterations
The following have been selected on the basis of their potential clinical significance (possible effect in parentheses where appropriate)—not necessarily inclusive (» = major clinical significance):

Table 2. Laboratory Value Alterations

With diagnostic test results» Gastric acid secretion test
(concurrent use of antacids may antagonize the effect of pentagastrin and histamine in the evaluation of gastric acid secretory function; administration of antacids is not recommended on the morning of the test)

Reticuloendothelial cell imaging of liver, spleen, or bone marrow with technetium Tc 99m sulfur colloid
(high doses of aluminum-containing antacids may impair reticuloendothelial cell imaging due to the polyvalent cations that cause agglomeration of the individual colloidal particles, thus causing them to be trapped by the pulmonary capillary bed rather than by the reticuloendothelial cells of the liver, spleen, and bone marrow) {34}

Skeletal imaging
(prior administration of aluminum-containing antacids may result in liver uptake of technetium Tc 99m pyrophosphate due to the formation of submicroscopic precipitates) {33}{86}

With physiology/laboratory test values

Calcium, serum
(concentrations may be increased with large doses) {68}{96}

Medical considerations/Contraindications
The medical considerations/contraindications included have been selected on the basis of their potential clinical significance (reasons given in parentheses where appropriate)— not necessarily inclusive (» = major clinical significance).

Table 3. Medical considerations/Contraindications

Note: A blank space usually signifies lack of information; it is not necessarily an indication that a given medical problem is of no concern. However, the pharmacologic similarity of these agents may suggest that if caution is required in particular medical problems for one agent, then it may be required for the others as well.

The medical considerations/contraindications included have been selected on the basis of their potential clinical significance (reasons given in parentheses where appropriate)—not necessarily inclusive (» = major clinical significance).

* Aluminum hydroxide has the ability to form the insoluble complex of aluminum phosphate, which is excreted in the feces. This may lead to lowered serum phosphate concentrations and phosphorus mobilization from the bone. If phosphate depletion (e.g., malabsorption syndrome) is already present, osteomalacia, osteoporosis, and fracture may result, especially in patients with other bone disease. {30}{79} In such patients predisposed to phosphate depletion, other aluminum-containing antacids (except aluminum phosphate) will be of concern only in relation to their ability to form an aluminum phosphate complex† Antacids containing more than 5 mEq (115 mg) of sodium per total daily dose should not be used without first checking with physician. The usual amount of sodium allowed in restricted diets is 3 grams or less per day‡ In patients with renal function impairment, use of antacids containing more than 50 mEq (608 mg) of magnesium per total daily dose should be carefully consideredPatient monitoringThe following may be especially important in patient monitoring (other tests may be warranted in some patients, depending on condition; » = major clinical significance):

With prolonged use or large doses and/or in renal diseaseHypermagnesemia or other electrolyte imbalance (dizziness or lightheadedness; irregular heartbeat; mood or mental changes; unusual tiredness or weakness) {31}

* Differences in frequency of occurrence may reflect either lack of clinical-use data or actual pharmacologic distinctions among agents (although their pharmacologic similarity suggests that side effects occurring with one may occur with the others). M = more frequent; L = less frequent; R = rare; U = unknown† May also occur with large doses and/or in chronic renal failure with calcium carbonate‡ Osteomalacia and osteoporosis have been reported after chronic ingestion of large doses of aluminum hydroxide–containing antacids. {30}{79} Since magaldrate is converted to aluminum and magnesium hydroxides in vivo , it is likely that osteomalacia and osteoporosis may occur with excessive use of magaldrate§ Chronic administration of magnesium trisilicate may infrequently produce silica renal stones.

Patient Consultation

Table 6. Patient Consultation

As an aid to patient consultation, refer to Advice for the Patient, Antacids (Oral).
In providing consultation, consider emphasizing the following selected information (» = major clinical significance):

For antacid use
The dose of antacid needed to neutralize gastric acid varies among patients, depending on the amount of acid secreted and the buffering capacity of the particular preparation. {69}

It is estimated that 99% of the gastric acid will be neutralized when a gastric pH of 3.3 is achieved. {69}

The amount (in mEq) of 1 N hydrochloric acid that can be titrated to pH 3.5 in 15 minutes by a certain dose of antacid is referred to as the neutralizing capacity of the antacid. {93} Approximately 15 to 20 mEq of an aluminum- and magnesium-containing antacid are required to neutralize 1 mEq of gastric hydrochloric acid.

Patients with hypersecretory disorders (e.g., duodenal ulcer, Zollinger-Ellison syndrome, multiple endocrine adenomas, and systemic mastocytosis) may require 80 to 160 mEq of buffer at each dose for symptomatic relief; this is approximately 30 to 60 mL of most antacids. {103} Only half of this dose is needed for patients with normal acid secretion.

The liquid dosage form of antacids is considered to be more effective than the solid or powder dosage form. {69} In most cases, tablets must be thoroughly chewed before being swallowed; otherwise, they may not dissolve completely in the stomach before entering the small intestine. {81}

The maximum recommended dosage should not be taken for more than 2 weeks, except under the advice or supervision of a physician. {69}

Combinations of antacids containing aluminum and/or calcium {105}{106}{107} compounds with magnesium salts may offer the advantage of balancing the constipating qualities of aluminum and/or calcium and the laxative qualities of magnesium. {69}

For use in peptic ulcer
In the treatment of peptic ulcer disease, to achieve adequate antacid effect in the stomach at the optimum time, most antacids are administered 1 and 3 hours after meals for prolonged acid-neutralizing effect and at bedtime. However, when taken at bedtime, their effect is not prolonged because of rapid gastric emptying. {93} Additional doses of antacids may be administered to relieve the pain that may occur between the regularly scheduled doses. {69}

Antacid therapy should be continued for at least 4 to 6 weeks after all symptoms have disappeared {69}, since there is no correlation between disappearance of symptoms and actual healing of the ulcer.

Aluminum hydroxide:
In the treatment of peptic ulcer, 960 mg to 3.6 grams are given orally every one or two hours during waking hours, the dosage being adjusted as needed. {69} For extremely severe symptoms of peptic ulcer (hospitalized patients), 2.6 to 4.8 grams diluted with two to three parts of water may be given intragastrically {69} every thirty minutes for periods of twelve or more hours a day.

For antihyperphosphatemic use

Aluminum hydroxide:
In adults, 1.9 to 4.8 grams of aluminum hydroxide are given orally three or four times a day in conjunction with dietary phosphate restriction. {104} In children, a dose of 50 to 150 mg per kg of body weight is given in four to six divided doses in conjunction with dietary phosphate restriction. {102}

For antiurolithic use

Aluminum carbonate:
In the prevention of phosphate stones the equivalent of 1 to 3 grams of aluminum carbonate is given four times a day, one hour after meals and at bedtime.

Oral Dosage Forms

Strength(s) usually available
U.S.—Additional information:

Table 7. Oral Dosage Forms

Note: Content and acid neutralizing capacity per capsule, tablet, or 5 mL, unless otherwise stated.
All products are available over-the-counter (OTC) in the U.S. and/or in Canada.

* Specific formulations may vary among the different manufacturers; check product labeling† In peptic ulcer disease, maximum therapeutic response may be obtained if taken 1 and 3 hours after meals and at bedtime. Severe symptoms may require more frequent dosing‡ Pediatric doses may range between 5 and 15 mL every 3 to 6 hours or 1 and 3 hours after meals and at bedtime, unless otherwise stated. However, these are general guidelines; proper diagnosis and dose individualization should precede the use of an antacid in a pediatric patient§ For appropriate Packaging and storage and Label information refer to designated letters as follows: